Non-Destructive Assessment of the Dynamic Elasticity Modulus of Eucalyptus nitens Timber Boards

Eucalyptus nitens is a fast-growing wood species with a relevant presence in countries like Australia and Chile. The sustainable construction goals have driven the search of structural applications for Eucalyptus nitens; however, this process has been complicated due to the defects usually presented in these timber boards. This study aims to evaluate the dynamic elasticity modulus (Exd) of Eucalyptus nitens timber boards through non-destructive vibration-based tests. Thirty-six timber boards with different levels of knots and cracks were instrumented and tested in a simply supported condition by measuring longitudinal and transverse vibrations. In the first stage, the Exd was calculated globally through simplified normative formulas. Then, in a second stage, the local variability of the Exd was estimated using operational modal analysis (OMA), finite element numerical simulations (FEM), and regional sensitivity analysis (RSA). The positive correlation found between the global static modulus of elasticity and Exd suggests that non-destructive techniques could be used as a reliable and fast alternative for the assessment of bending stiffness. Finally, the proposed method to estimate the local variability of Exdt based on the combination of OMA, FEM, and RSA techniques was useful to improve the structural selection process of timber boards for lightweight social housing floors.

Modelling of Airport Rigid Pavement for Complex Configuration of Landing Gears and for a Large Spectrum of Cement Concrete

The purpose of this paper is to develop new design diagrams in order to complete the actual Romanian standard. This addendum is justified by the fact that the current design diagrams are elaborated for a single value of the E - dynamic elasticity modulus (in Romanian standard E = 30000 MPa) and of the Poisson ratio (in Romanian standard ν = 0.15). Therefore the diagrams from the Romanian standard NP034-99 do not permit the design for other types of concrete cement with improved characteristics with elasticity modulus E 30000 until E = 50000 MPa or of the Rolled Compacted Concrete (RCC) with Poisson ratio ν = 0.25 or of the other concrete types as cement concretes with recycled aggregates or steel fibre reinforced concrete. The first part of the paper presents the stress design methodology based on the finite element software and on the parameters which interfere in the design calculation. In addition to the diagrams from the Romanian standard which apply only to an external load up to a four wheel bogie, the diagrams with loads with six wheel bogie are introduced. Further are shown the differences between the stress calculated with single values from the actual Romanian standard and the stress calculated with the exact values of the considered parameters [E dynamic elasticity modulus and the Poisson ratio]. The study relies on the specific load of modern aircrafts (like Airbus - A380, Boeing - B777) that have six footprints tire in the landing gear structure. In the end, the article brings forward a graphic comparison analysis between the diagrams of the Romanian current standard and the ones conducted in the present study by using FEM (Finite Element Method). Furthermore, a design case study exemplifies the method used to obtain the slab thickness for an airport rigid pavement structure using an external load from a complex landing gear with six footprints tire.

Experimental Research on Resistance to Frost of Rubberized Concrete

According to mixture proportions design, rubber concrete specimens were produced, which were used for test of resistance to frost. In this study, different grain size and different content rubber were mixed in Portland cement concrete. Quick freeze-thaw test was carried to rubberized concrete. The research shows that appropriate proportional fine aggregate replaced by the discarded tires powder and grain can improve concrete resistance to frost, although concrete compressive strength, flexural strength and dynamic elasticity modulus decrease with increasing of rubber content. The improving effect of rubber powder is better than rubber grain. Furthermore, it is demonstrated that the dynamic elasticity modulus obtained by Non-destructive testing can commendably evaluate the frost resistance of rubberized concrete.

Behaviour of Cement and Polymer Mortar Materials to Rapid Freeze-Thaw Cycling

The aim of this investigation work is threefold: 1) To analyse and quantify freeze-thaw resistance of glass fibre reinforced epoxy polymer mortars, comparatively to both normal cement mortars and plain epoxy polymer mortars; 2) To determine glass fibre reinforcement effect on freeze-thaw behaviour; and 3) To evaluate the reliability of ASTM C666M-03 test methodology for the assessment of freeze-thaw resistance of polymer concrete materials. For this purpose several test specimens, normal cement mortars, plain and glass-fibre reinforced epoxy polymer mortars were submitted to freeze-thaw cycling between 36 up to 300 cycles, according to the above norm. Dynamic elasticity modulus, with basis on fundamental resonance frequency measurements, was calculated every 36 cycles, and the correspondent relative dynamic elasticity modulus was determined for each cycling period. In order to assess the reliability of this non-destructive test methodology, three specimens of each formulation were withdrawn at regular periods and tested in bending and compression. Relative mechanical strengths, as function of conditioning period, were compared with corresponding relative dynamic modulus of elasticity.